I’m unaware of _any_ illness where some measure of immunity is not developed. I find it incredibly hard to believe that recovering from covid infection does not afford some level of immunity.

I do wonder if recovery due to anti-virals prevents or weakens immunity, however.

Right. If our immune system didn't get better at fighting something, you would remain infected forever or die from it. Reference HIV as an example of a virus our immune system could not fight.

If anyone is getting better (and 98%+ of people are) it's because the immune system can effectively fight it.

Wow, I didn’t even think of it like that. That’s a great way to reason about it that makes it immediately clear. Thanks!

Or it could go dormant, like the herpes virus.

Maybe it's sort of survivor bias. Maybe antivirals don't weaken immunity but people who survived thanks to antivirals have innately such a weak immune response that they wouldn't have survived without them.

Huh? Antivirals just eliminate the virus before the immune system gets a chance to step in and build up immunity. How about that?

I don't think that's true. I don't think they give antivirals to people before they have fever.

And fever is one of the results of immune system working.

Sure, but the body still isn't done building up immunity.

Miniscule amount of pathogen in the vaccine can give you full immunity. I think when you have fever your immune system was already exposed to enough of the virus to build full immunity for the future. Now it's just the case of whether you survive to enjoy your future immunity. And anti-virals just help you with that part.

Okay, I'm not a doctor, so maybe you're right. It just doesn't seem plausible. Though, that doesn't mean much.

Your prior should be that immunity works as it does with every other virus and you should require very strong evidence to the contrary (evidence, not anecdotes) to convince you otherwise. Throughout our evolutionary history we have come into contact with innumerable viruses and to a greater or lesser extent we have immunity to all of them post exposure. For many our immunity is long lived, on the order of years.

It's not a boolean whether people become immune or not--maybe some small portion of the population have issues developing immunity and the rest are fine?

My reasoning is the same, but rather than it being binary, it’s a gradient.

So after recovery I might be able to ward off 80% of exposure events that would infect a non-immune person. But given enough exposures or just really bad luck, I could still get infected again.

That being said generally in these cases the infection resolves way sooner due to the same mechanism that leads to immunity: immune “memory cells” which wait dormant, ready to start production of immune cels when exposed to the characteristic antigens

With any non-negligible immunity rate (for example, 70% would be typical for immunity gained through an influenza vaccine [0]), we will still see exponential decay once a critical mass (R0 < 1) is reached. I believe immunity rates are higher after recovering from real infections, but still not perfect.

Therefore a headline reading "Japanese man gets reinfected" is not of particular concern while "50% of survivors get reinfected" would be highly concerning.

[0] https://www.ecdc.europa.eu/en/seasonal-influenza/prevention-...

Interesting, I wasn’t aware immunity works this way. Thanks

the models already account for this. eg in compartmental models both SIS or SIRS have this assumption.

Doesn’t swine flu recur every now and then? Every virus could potentially become endemic.

Is it at all possible that we become progressively more immune with each incidence or that we can only be infected N times? If either of these things are true our strategy will still work.

Viruses do mutate. So for many people, the body may never develop complete immunity.

SARS (including this new Coronavirus) does not mutate nearly as fast as the flu and other viruses though. It has built in error correction, and this is good news for us:

> But SARS has a molecular proofreading system that reduces its mutation rate, and the new coronavirus’s similarity to SARS at the genomic level suggests it does, too. “That makes the mutation rate much, much lower than for flu or HIV,” Farzan said. That lowers the chance that the virus will evolve in some catastrophic way to, say, become significantly more lethal.

https://www.statnews.com/2020/02/04/two-scenarios-if-new-cor...